The simplest way to check spice quality is to match each likely adulterant to a test, then have a lab confirm anything the screening test flags. A cumin adulteration test looks for grass seed, stems or dyed material. Fennel seed colour is checked by comparing extracts. Chilli powder adulteration is checked for added dyes, starch and brick powder.
Visual checks are a first filter, not proof. For a contract, specify the tests and the limits in writing.
Cumin adulteration tests
Cumin can be mixed with similar-looking seeds, stems and foreign matter, or coloured to look fresher. Look for uneven seed shape, grass seed, dust and unusual colour. A lab can measure foreign matter, ash and acid-insoluble ash, and can examine the sample under a microscope.
Our article on how cumin is adulterated and how to detect it gives the signs to look for.
Fennel seed colour adulteration
Fennel seed is sometimes coloured green to look fresher. A simple screening test is to rub the seeds on white paper or soak a sample in water or a solvent and look for colour in the liquid.
A positive screening result should go to a laboratory, which can identify the dye. See colour added to fennel seed for how to check.
Chilli powder and turmeric adulteration
Chilli powder can contain added oil-soluble dyes, which a lab detects by chromatography. It can also contain starch, sawdust or brick powder, which show in simple dilution tests and in ash measurements.
Turmeric has a long history of lead chromate adulteration to intensify colour. Lead chromate is toxic. A lab test for lead and a visual check of the colour are the standard control. Many buyers specify a maximum lead level in the contract and test every lot. More methods are in detecting starch and colour adulteration in spice powders.
Matching test to adulterant
- Foreign matter and extraneous seed: sieving, visual grading and a lab foreign matter test.
- Added soluble dyes: solvent extraction screening, then chromatography at a lab.
- Added starch: iodine screening or microscopy.
- Mineral adulterants: total ash and acid-insoluble ash.
- Toxic metals, such as lead in turmeric: lab analysis, usually by atomic spectroscopy.
How to check spice quality in practice
Write the specification and test list into the contract, ask for a pre-shipment sample from the actual lot, and have an independent accredited lab test it. Compare the lab sample with the approved sample and retain a sealed sample from each lot.
The certificate of analysis from the supplier is not a substitute. See how to read a lab certificate for what to check.
What a lab result cannot tell you
A clean result applies to the sample, not to every bag in the lot. Adulteration is often patchy, and a few bags from the top of a stack can look fine. That is why sampling matters as much as the test itself.
Draw samples from several points across the lot, mix them and split the sample into sealed portions, one for the lab, one for you and one kept for any later dispute. Also check the trader's story. A seller who cannot say where the seed was cleaned or ground is a higher risk, as explained in how to tell a trader from a manufacturer.
Next step
We choose the tests with you, draw samples from the lot and send them to an accredited lab. To set up testing on your first order, book a free sourcing review.